Perry Denehy, M.Ed., the lead athletic trainer for Sycamore High School, cautions young athletes and their coaches to be aware of the effect of heat on the body.

“As an athletic trainer, what I’m watching for in the athlete is those that are showing some type of fatigue," he said. "Their energy level is down, and, of course, anything like vomiting or excessive sweating.”

Denehy has worked as a trainer for over 30 years and is now employed by TriHealth.

WATCH: See how Denehy explains the stages of heat illness in the video player above

He says the first sign of heat stress is muscle cramping, possibly in the calf or stomach. If players don’t rest and cool down at this point, they could develop heat exhaustion or heat stroke.

“Heat exhaustion is when the body systems start to fail. Fatigue, dizziness, maybe loss of consciousness will occur,” says Denehy. “Heat stroke is where the body has run out of all cooling mechanisms and the core body temperature can exceed 110 degrees.”

“That needs to be treated as a medical emergency, calling 911, cooling the body as quickly as possible.”

Stop activity, move to a shaded area, and try to cool the body by removing some clothing and applying ice packs until emergency crews arrive.

To help prevent heat illness and ensure safety, coaches can check conditions on the playing field before practices and games, using a heat index monitor. The heat index is what the temperature feels like to the human body when relative humidity is combined with air temperature, according to the National Weather Service.The body feels warmer during humid conditions.

“When the heat index climbs too high, it’s going to be an alert to those staff to get the athletes indoors,” says Denehy.

“The Ohio High School Athletic Association recommends that any time the heat index is above 100, we have players move indoors,” says Denehy. “Below 100, we take extra precautions; recommend more frequent water breaks; and take off additional equipment if possible.”